This application is based on and claims priority under 35 U.S.C. sctn. 119 with respect to Japanese Applications No. 2002-096620 and No. 2002-096621 both filed on Mar. 29, 2002 the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a vehicle control device incorporating an electric power steering device with an electric motor for generating an assist force when a steering wheel is manipulated by the driver. More particularly, it relates to a vehicle control device with the power steering device for automatically suppressing or moderating a yaw motion acting on a vehicle.
2. Discussion of the Related Art
FIG. 10 exemplifies a control block diagram of a prior art operation processing procedure for an ACT (actuator) command angle (xcex41). The ACT command angle (xcex41) has been used as a compensation amount for the real steering angle of front wheels for the purpose of automatically suppressing or moderating a yaw angular motion which is caused by a disturbance.
A vehicle state inference section infers a target value (rn) of a vehicle yaw angular velocity (r) and a target value (xcex1n) of a vehicle side slip angle (xcex1) based on a measured steering angle (xcex8H) and a measured vehicle speed (V) of the vehicle. The yaw angular velocity (r) and the side slip angle (xcex1) of the vehicle are further measured and the aforementioned ACT command angle is calculated based on the following equation (1). Thus, as a result of the real steering angle (xcex4) of the front wheels being adjusted automatically, the yaw angular motion which is caused by a disturbance is relieved, to some extent, of the part exceeding the level to be suppressed.
xcex41=g1(rnxe2x88x92r)+g2(xcex1nxe2x88x92xcex1)xe2x80x83xe2x80x83(1)
The equation above is high in applicability and has a relatively wide range of application. However, it was found by our experiment that as long as the equation (1) is used under an unusual situation, the yaw angle motion of a magnitude which exceeds a critical level at the occurrence of a disturbance cannot be necessarily suppressed to a satisfactory level.
Especially, in applying the equation (1) in the case of straight-ahead running at high speeds, the accuracy in calculation is low with the compensation amount constituting an ACT (actuator) command angle (xcex41). Thus, where the foregoing prior art method is employed in calculating the compensation amount on the basis of the foregoing equation (1), it was not easy to satisfactorily realize the vehicle motion performance having a rigid straight-ahead stability.
Further, in the prior art, the feedback control of the yaw angular velocity (r) is executed in a well-known proportional control method.
In the present sensing technology, it is not easy to calculate the aforementioned difference (xcex94rxe2x89xa1rnxe2x88x92r) satisfactorily precisely. This gives rise to problems in the following respects.
(Problem 1) Since the aforementioned difference (xcex94r) involves an error, it may occur that if the gain (g1) of the above equation (1) is increased, an unpleasant feeling such as vibration, an unusual or strange steering feeling or the like is given to the driver. This makes it difficult to increase the gain (g1) as much large as needed.
In addition, if the control mode of executing the feedback control of the yaw angular velocity (r) is altered from a proportional control to a conventional proportional integral control, a further problem occurs in the following respect.
(Problem 2) It may occur that the time-integration of the difference (xcex94r) invites cumulating the above error thereby to lower the calculation result in accuracy. As a consequence, it may further occur that the driver is given a steering feeling accompanied by an unusual or strange feeling. Moreover, the error in the time-integration may be enlarged as time goes. Therefore, a favorable result is quite difficult to realize only by altering the control mode from the proportional control to a conventional proportional integral control.
For the reason that the foregoing problems and in particular, the problem 2 are not easy to solve, the proportional control mode has heretofore been employed with respect to the yaw angular velocity (r).
For example, when braking is applied with a vehicle traveling on a asymmetrical surface road having an asymmetrical surface state, the difference (xcex94r) or the difference (xcex1nxe2x88x92xcex1) increases. If an attempt is made to execute the vehicle control depending on the above equation (1) under the circumstance as mentioned above, the vehicle would try to follow a target line of traveling as it makes a large vibration. In this event, the driver tries to keep the vehicle in parallel to the asymmetrical surface road by holding the neutral steering position or by performing a counter steering against the yawing. However, the steering optimum to the circumstance is not easy to perform, and therefore, it comes often to the case that the vehicle makes a large angle with respect to the traveling road.
It is therefore a primary object of the present invention to provide an improved vehicle control device capable of realizing a vehicle motion performance which is rigid or stiff in a straight-ahead stability and is sufficiently stable.
Another object of the present invention is to provide an improved vehicle control device capable of being rigid or stiff against a yaw motion acting on a vehicle.
A further object of the present invention is to provide an improved vehicle control device capable of suppressing or moderating a yaw motion acting on a vehicle within a short period of time.
A still further object of the present invention is to provide an improved vehicle control device capable of enhancing the traveling stability of a vehicle on a road having an asymmetrical surface state.
Briefly, according to the present invention, there is provided a vehicle control device including a power steering device which provides an assist torque or a steering angle command to a steering mechanism of a vehicle, the control device comprising: compensation steering angle operation means for calculating a compensation steering angle relative to a real steering angle of the steering mechanism; extraordinary yaw motion detecting means for detecting the occurrence of an extraordinary yaw motion which is not caused by the steering manipulation of the driver; compensation steering angle altering means for altering the compensation steering angle to suppress the extraordinary yaw motion; and real steering angle control means for controlling the compensation steering angle by using the compensation steering angle altering means when the occurrence of the extraordinary yaw motion is detected by the extraordinary yaw motion detecting means.
With this configuration, when the occurrence of the extraordinary yaw motion is detected, the compensation steering angle is altered to suppress or make relief of the extraordinary yaw motion, so that the straight-ahead stability of the vehicle can be improved.
In another aspect of the present invention, as defined in claim 2, the extraordinary yaw motion detecting means includes straight-ahead steering judging means for making judgment as to whether or not the driver is steering the vehicle to travel straight ahead, and the extraordinary yaw motion detecting means detects the occurrence of the extraordinary yaw motion not caused by the steering manipulation of the driver when he or she is manipulating the straight-ahead steering.
With this configuration, the yaw motion caused by a disturbance is distinguished from that intentionally caused by the driver, and the vehicle control is performed depending on the distinction. Therefore, the straight-ahead stability can be secured while the maneuvering in a sports-like driving can also be maintained at the same time.
In another aspect of the present invention, as defined in claim 3, the device further comprises object detecting means for detecting an obstacle or a moving object existing around the vehicle, and first compensation canceling means for canceling the compensation operation by either causing the compensation steering angle operation means not to operate or making the compensation steering angle zero when the obstacle or the moving object is detected by object detecting means.
With this configuration, when an obstacle or a moving object existing around the vehicle is detected, the compensation steering angle operation is substantially cancelled, so that the driver is able to maneuver the vehicle to cope with an emergency situation.
In a further object of the present invention, as defined in claim 6, the device is constructed such that the extraordinary yaw motion detecting means detects the extraordinary yaw motion occurring when the vehicle is braked on a road which is asymmetrical with respect to the right and left surface states thereof.
With this configuration, the vehicle control device is given a capability of detecting whether or not brake is applied on the vehicle traveling on a road having an asymmetrical character of the surface state. Thus, the vehicle control device is able to make the vehicle adapted to such a road.